Spring-balanced or weight-balanced loading arms are generally used for transferring wet or dry materials into tank cars or trucks. The spring-balanced loading arms shown in U.S. Pat. Nos. 3,244,440 issued to Albert A. Ashton et al. on Apr. 15, 1966 and U.S. Pat. No. 4,537,233 issued to Evart J. Vroonland on Aug. 27, 1985 are examples of loading arms which are currently in use. These loading arms have a tendency to rise out of the truck or tank car loading port during loading because of the force of the counterbalance spring or the counterbalance weight and the jet action of the material being discharged. For safety reasons, it is very desirable to lock the loading arm when it is used for transferring a material. Absent any locking mechanism, the loading arm will have an unwanted vertical and horizontal movement during loading operations. These movements are aggravated when the loading is being done into an open dome type tank car or truck.
In the past, locking devices have been used to lock down the loading arm at the riser end of the arm. However, these devices require the loading arm operator to move from his position at the loading port to the riser end to engage the locking device. Furthermore, these lock-down devices still permit a certain amount of movement of the loading arm at the port end.
The present invention provides a lock-down device which positively locks a loading arm into a given position during loading operations.